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Biomedical subjects

D Roberts

Publications and source records attributed to D Roberts.

At least 73 records · Page 4Linked to original sources
PubMed2000

The role of gamma knife surgery in the treatment of severe epilepsies.

There is a strong rationale for investigation of the role of gamma knife radiosurgery in the treatment of medically intractable epilepsy. To explore this potential application, the current outcome and morbidity associated with established microsurgical treatment, as well as the associated advantages and disadvantages of open surgery, are reviewed. The preliminary evidence in support of radiosurgical treatment and the recent experience with gamma knife treatment for epilepsy associated with mesial temporal sclerosis, cavernous angioma, and hypothalamic hamartoma or other lesions are presented. The strengths and limitations of this application are discussed, and the challenges facing both microsurgical and radiosurgical approaches are considered. Gamma knife surgery can be a main approach among others in the armamentarium of epilepsy surgery. Although the benefits of comfort and reduced invasivity can be clearly perceived, larger series and long-term follow up are still required in order to evaluate the future of this particular surgical approach.

Epilepsy↗
PubMed2000

Guidelines for the microbiological quality of some ready-to-eat foods sampled at the point of sale. PHLS Advisory Committee for Food and Dairy Products.

These guidelines for the microbiological quality of ready-to-eat foods represent a revision and expansion of guidelines first published by the PHLS in September 1992 and revised in March 1996. The latest guidelines incorporate many of the constructive comments received from food examiners and other microbiologists within and outside the PHLS and from environmental health officers throughout the United Kingdom. This document reviews the changes and the reasons they were made and sets out the new guidelines. It also clarifies the role of food examiners in interpreting the microbiological results of formal samples.

Colony Count, Microbial↗
PubMed1999

Use of solid-phase microextraction for measuring oil-water partition coefficients and correlation with high-performance liquid chromatographic methods for lipophilicity.

For flavour compounds, lipophilicity is often estimated by the partition coefficient between oil and water (log Koil-water), which is highly relevant to food. A modification of the shake-flask method is reported here where compounds are quantified in the two phases using solid-phase microextraction (SPME). SPME's highly sensitivity to non-polar compounds facilitates quantification in the water phase. Twelve flavour compounds representing a broad range of lipophilicities and functional groups were analysed by two methods. Their log Koil-water was determined using SPME quantitation and their log k(w) using a reversed-phase HPLC methodology. The isocratic capacity factor at 60% methanol and predicted log P value also showed high correlation factors with other methods. The octadecyl silylated surface of the HPLC column provides a matrix that interacts with lipophilic compounds where the retention time is the indication of lipophilicity. Both methods gave reproducible results (median 3% and 4% RSD) and similar but not identical values for lipophilicity. The relationship between the two methods is log k(w) =0.85 log Koil-water +0.48 with a correlation coefficient of 0.94. The new SPME detection method, with the ability to quantify limonene and 2-pentylfuran at 1 ppm in the water phase, is preferred for flavour compound analysis due to the applicability of oil-water partitioning in food.

Buffers↗
PubMed1999

The human granulocyte-macrophage colony-stimulating factor gene is autonomously regulated in vivo by an inducible tissue-specific enhancer.

The granulocyte-macrophage colony-stimulating factor (GM-CSF) gene is part of a cytokine gene cluster and is directly linked to a conserved upstream inducible enhancer. Here we examined the in vitro and in vivo functions of the human GM-CSF enhancer and found that it was required for the correctly regulated expression of the GM-CSF gene. An inducible DNase I-hypersensitive site appeared within the enhancer in cell types such as T cells, myeloid cells, and endothelial cells that express GM-CSF, but not in nonexpressing cells. In a panel of transfected cells the human GM-CSF enhancer was activated in a tissue-specific manner in parallel with the endogenous gene. The in vivo function of the enhancer was examined in a transgenic mouse model that also addressed the issue of whether the GM-CSF locus was correctly regulated in isolation from other segments of the cytokine gene cluster. After correction for copy number the mean level of human GM-CSF expression in splenocytes from 11 lines of transgenic mice containing a 10.5-kb human GM-CSF transgene was indistinguishable from mouse GM-CSF expression (99% +/- 56% SD). In contrast, a 9.8-kb transgene lacking just the enhancer had a significantly reduced (P = 0.004) and more variable level of activity (29% +/- 89% SD). From these studies we conclude that the GM-CSF enhancer is required for the correct copy number-dependent expression of the human GM-CSF gene and that the GM-CSF gene is regulated independently from DNA elements associated with the closely linked IL-3 gene or other members of the cytokine gene cluster.

Animals↗
PubMed1999

Expression, characterization, and crystallization of the pyrophosphate-dependent phosphofructo-1-kinase of Borrelia burgdorferi.

The two genes for the putative pyrophosphate-dependent phosphofructokinases (PPi-PFKs) of Borrelia burgdorferi were cloned by PCR and expressed in Escherichia coli, and their protein products were purified to near homogeneity. The larger of the two gene products, a 62-kDa protein, is an active PPi-PFK and exists in solution as a dimer. It has apparent K(m) values for fructose 6-P and PPi of 109 and 15 microM, respectively, and a pH optimum of 6.4 to 7.2. The 62-kDa protein was crystallized and subjected to preliminary diffraction analysis. The smaller gene product, a 48-kDa protein, exists in solution as a higher polymer and shows no ATP- or PPi-dependent activity, despite having a secondary structure as estimated by circular dichroism that is not significantly different from that of other PFKs.

Animals↗
PubMed1999

Ethical and practical considerations of withdrawal of treatment in the intensive care unit.

PURPOSE: To discuss the medical, ethical and legal basis of decisions to discontinue life-support therapy in the adult intensive care unit (ICU), and to provide practical guidelines for the discontinuation of life support therapy. SOURCE: Relevant articles were retrieved through Medline (1991-present; terms: ethics, life support discontinuation, double effect, beneficence, non-maleficence). Other sources include legal references, and personal files. PRINCIPAL FINDINGS: Understanding the legal and ethical principles of autonomy, beneficence, non-maleficence and double effect are crucial when withdrawing life support therapy. The law respects a competent patient's right to direct his/her healthcare but does not uphold his/her right to demand futile care. Surrogate decision makers can be used when the patient is incompetent, provided they are acting in the patient's best interest. Euthanasia is illegal and the distinction between discontinuation of therapy and euthanasia is legally clear. Skillful administration of palliative therapy cannot be construed as euthanasia when the aforementioned ethical principals are respected. The various practical methods of discontinuing therapy are discussed. Every ICU should develop its own guidelines and a checklist to help caregivers during this difficult time. Caregivers must anticipate the mechanism of death and direct interventions at the symptoms that are likely to cause discomfort. Drugs and dosages must be individualized, and depend on the underlying disease, anticipated mechanism of death, and the patient's pharmacological history. When prescribing a drug, the intention should be clear. CONCLUSIONS: Appropriate discontinuation of therapy in the ICU allows patients a dignified and comfortable death.

Dissent and Disputes↗
PubMed1999

Proprioceptive defects after an anterior cruciate ligament rupture -- the relation to associated anatomical lesions and subjective knee function.

A disturbed proprioception has been described in patients with an anterior cruciate ligament (ACL) deficient knee. The relation to demographic data and to different commonly associated anatomical lesions, as well as to subjective knee function, was prospectively studied in 16 consecutive patients after an acute knee ligament injury. All patients had a complete rupture of the ACL, but variable associated anatomical lesions. The threshold to detect a passive motion, as a measure of their proprioceptive ability, was registered repeatedly during the first year after injury. Four of the patients had consistently severe and persistent deficits at 1, 2 and 8 months. These four individuals had more chondral lesions and a lower subjective rating of their knee function than the remaining patients. In the whole group there were significant correlations between the recorded thresholds and associated chondral lesions, meniscal lesions and the subjective rating of knee function. We found no significant relation between age, gender, activity level, grade of mechanical laxity increase or a medial collateral ligament rupture, and the proprioceptive recordings. Thus, morphological lesions other than a rupture of the ACL seem to contribute to the proprioceptive deficits after a knee ligament injury, and the patients' ability to detect a passive motion showed a relation to subjective knee function from the time of injury onwards.

Adolescent↗
PubMed1999

The nondiagnostic ECG in the chest pain patient: normal and nonspecific initial ECG presentations of acute MI.

The 12-lead electrocardiogram (ECG) is a powerful clinical tool used in the evaluation of chest pain patients, assisting in the selection of the proper therapy. Unfortunately, the ECG is diagnostic of acute myocardial infarction (AMI) in only one-half of such patients at initial hospital evaluation. In the remaining group of patients with the nondiagnostic 12-lead electrocardiogram, the ECG may be entirely normal, show nonspecific sinus tachycardia (ST) segment-T wave abnormalities, or obvious ischemic changes. In adult chest pain patients treated in the emergency department (ED), 1% to 4% of such patients with an absolutely normal ECG had a final hospital diagnosis of AMI; furthermore, patients with nonspecific electrocardiographic abnormalities experienced AMI in 4% of cases. These findings reinforce the teaching point that the history is the most important tool used in the evaluation of chest pain patients. Furthermore, overreliance on a normal or nonspecifically abnormal ECG in a patient with a classic description of anginal chest pain is dangerous.

Aged↗
PubMed1999

Plasticity-induced damage layer is a precursor to wear in radiation-cross-linked UHMWPE acetabular components for total hip replacement. Ultra-high-molecular-weight polyethylene.

The mechanism for the improved wear resistance of cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) remains unclear. This study investigated the effect of cross-linking achieved by gamma irradiation in nitrogen on the tribologic, mechanical, and morphologic properties of UHMWPE. The goal of this study was to relate UHMWPE properties to the wear mechanism in acetabular-bearing inserts. Wear simulation of acetabular liners was followed by detailed characterization of the mechanical behavior and crystalline morphology at the articulating surface. The wear rate was determined to be directly related to the ductility, toughness, and strain-hardening behavior of the UHMWPE. The concept of a plasticity-induced damage layer is introduced to explain the near-surface orientation of the crystalline lamellae observed in the wear-tested acetabular liners. Cross-linking reduces abrasive wear of acetabular components by substantially reducing--but not eliminating--the plasticity-induced damage layer that precedes abrasive wear.

Acetabulum↗
PubMed1999

Hemodialysis prognostic nutrition index as a predictor for morbidity and mortality in hemodialysis patients and its correlation to adequacy of dialysis. Council on Renal Nutrition National Research Question Collaborative Study Group.

OBJECTIVE: Prospectively examine the use of a hemodialysis prognostic nutrition index (HD-PNI) as a predictor for morbidity and mortality in hemodialysis patients and its correlation to adequacy of dialysis. DESIGN: Prospective randomized collaborative study group. SETTING: There were 211 chronic hemodialysis centers; 202 from 43 United States, 9 from Canada. PATIENTS: There were 1527 hemodialysis patients undergoing treatment a minimum of 3 months and at least 18 years of age. Sample mirrored United States Renal Data System data for age, sex, race, and etiology of renal failure. INTERVENTIONS: None; routinely collected demographic, biochemical, and clinical data for 8-month baseline and 3-month predictive phases. METHODS: HD-PNI calculated from baseline data as linear mathematical equation using level of serum albumin, level of serum creatinine, and number of days and times hospitalized; HD-PNI risk defined as >/=0.8. Adequacy of dialysis calculated as urea reduction ratio (URR) from baseline data; adequacy risk defined as URR of </=65%. MAIN OUTCOME MEASURES: Number of times and days hospitalized, mortality. RESULTS: For this research, 1167 patients completed the study (76%) with 360 (24%) dropped due to death, incomplete data, transfer, or change in modality. Patients completing study with HD-PNI risk (n = 208, 18%) compared with patients who had no HD-PNI risk (n = 959, 82%) were hospitalized more often (57.2% v 28.5%, P <. 01), hospitalized with infection more often (14.6% v 4.6%, P <.01), and had greater mortality (7.7% v 2.5%, P <.01). Stratification of HD-PNI risk by URR of >/=65% did not significantly improve prediction. CONCLUSIONS: Use of HD-PNI is an effective screening tool to identify hemodialysis patients at risk for morbidity and mortality. No correlation was found between URR and HD-PNI.

Adult↗
PubMed1999

Early parental interactions with and perceptions of multiple birth infants.

The perceptions and interactions of mothers and fathers of seven sets of twins and one set of triplets were compared to those of parents of 49 singleton infants. Couples were typically interviewed together three times during the pregnancy and at 1 week and 3 months post-partum. Two-weekly observations of mother-father-infant interactions were conducted after the first postnatal interview. Three major themes were apparent in the interviews--the positive and negative specialness for multiple births, difficulties involved in managing more than one infant, and attachment issues--that were also evident during the observations. Although there were few differences in care-giving and interactive behaviours between the multiple birth and singleton parents, the logistics of caring for more than one infant dictated that multiple birth infants were left alone more and looked at, talked to and held less often. Couples used different strategies to care for their infants, varying in both the extent to which they interacted preferentially with the infants and in the relative involvement of the mother, father and others.

Analysis of Variance↗
PubMed1999

Psychosocial care in oncology nursing: a study of social knowledge.

A combination of focus group and individual interviews aimed to examine psychosocial aspects of nursing within a social context and social knowledge held by two teams of ward-based oncology nurses. Five core categories of knowledge emerged: knowledge of how to care, knowledge of the patient, knowledge of the ward, knowledge of nurses coping, and knowledge of involvement. Involvement or emotional closeness was seen as a necessary, inevitable and potentially stressful feature of psychosocial care. The authors conclude that interpersonal and professional aspects of nursing must be balanced in order to provide effective psychosocial care.

Adaptation, Psychological↗
PubMed1999

Erythropoietin concentration and arterial haemoglobin saturation with supramaximal exercise.

The aim of this study was to determine if the hypoxaemic stimulus generated by intense exercise results in the physiological response of increased erythropoietin production. Twenty athletes exercised for 3 min at 109 +/- 2.8% (mean +/- s) maximal oxygen consumption. Estimated oxyhaemoglobin saturation was measured by reflective probe pulse oximetry (Nellcor N200) and was validated against arterial oxyhaemoglobin saturation by CO-oximetry in eight athletes. Serum erythropoietin concentrations-as measured using the INCSTAR Epo-Trac radioimmunoassay-increased significantly by 28 +/- 9% at 24 h post-exercise in 11 participants, who also had an arterial oxyhaemoglobin saturation < or = 91% (P < 0.05). Decreased ferritin levels and increased reticulocyte counts were observed at 96 h post-exercise. However, no significant changes in erythropoietin levels were observed in nine non-desaturating athletes and eight non-exercise controls. Good agreement was shown between arterial oxyhaemoglobin saturation and percent estimated oxyhaemoglobin saturation (limits of agreement = -3.9 to 3.7%). In conclusion, short supramaximal exercise can induce both hypoxaemia and increased erythropoietin levels in well-trained individuals. The decline of arterial hypoxaemia levels below 91% during exercise appears to be necessary for the exercise-induced elevation of serum erythropoietin levels. Furthermore, reflective probe pulse oximetry was found to be a valid predictor of percent arterial oxyhaemoglobin saturation during supramaximal exercise when percent estimated oxyhaemoglobin saturation > or = 86%.

Adult↗
PubMed1999

Effect of FK 506 and lipo prostaglandin E1 on heart allograft survival in rats.

FK 506 (FK) has a strong immunosuppressive effect, but a low-grade, dose-dependent nephrotoxicity and diabetogenicity, which means that reducing the dose of FK is of considerable interest. Lipo-prostaglandin E1 (LPGE1) is a preparation of PGE1 that has potent immunosuppressive properties, and its duration of action is longer than that of ordinary PGE1. The purpose of this study was to investigate whether LPGE1 can enhance the immunosuppressive effect of FK. Heterotopic cardiac transplantations to the neck vessels were performed, and recipient rats were treated with intramuscular injections of FK and LPGE1 once daily for 10 days. All grafts without any treatment were rejected within 14 days. In comparison, the FK doses of 0.07, 0.2 and 1.0 mg/kg/day for 10 days significantly increased the long-term graft survival (>100 days) to 8%, 44% and 100%, respectively. The addition of LPGE1 to the first two dosages caused a further significant increase in the graft survival, to 18% and 80%, respectively, when compared with the control. LPGE1 appears to enhance the immunosuppressive effect of FK.

Alprostadil↗
PubMed1999

Intraoperative assessement of coronary flow and coronary vascular resistance during coronary bypass surgery.

The measurement of coronary graft flow rates is a well-established method of assessing graft function intraoperatively. In order further to understand the dynamics of graft function, the resistance to the flow was considered a desirable measurement intraoperatively. The coronary vascular resistance (CVR) was estimated by applying the Poiseuille-Hagen equation. The CVR was estimated at zero cardiac work (during cardioplegic arrest) using fixed perfusion flow rates and estimating the pressures produced. After going off cardiopulmonary bypass (CPB), the bypass graft flow (F) was estimated by a standard ultrasound Doppler technique. The perfusion pressure over the perfused coronary graft was then determined and the CVR in the working heart ascertained. The CVR was studied in 178 vein grafts in 59 patients undergoing coronary bypass surgery. The mean CVR in the cardioplegic heart (c-CVR) varied from 0.81 to 2.3 mmHg/ml/min for various coronary artery diameters and was significantly higher in small diameter arteries compared with larger arteries (p < 0.0002). Consequently significant high flows were found in the large vessels compared with the smaller ones (p < 0.0001). The mean c-CVR during cardioplegia of 1.57 +/- 0.06 increased significantly to 1.75 +/- 0.07 mmHg/ml/min after the procedure (p-CVR) and was attributed to the dynamic resistance of the working heart. The post-CPB graft flow was significantly and negatively correlated to the c-CVR of the arrested heart. The measurement of coronary vascular resistance reveals coronary beds at potential high risk for inadequate perfusion. Such areas are usually fed by small vessels with low flows. The working heart, in turn, increases the coronary resistance following cardioplegia during the surgical procedure.

Adult↗